Counter-offensives by Iraqi and Kurdish armed forces, supported by the U.S.-led coalition, and by Iran-backed Shiite militias have forced ISIS out of several cities — including Tikrit, north of Baghdad, and Ramadi, to the west last month.

In Syria, ISIS is fighting the army of President Bashar Assad and other rebel groups opposed to his rule.

It is facing air strikes by the U.S.-led coalition and by Russia which has sent warplanes to support its ally, the Syrian government. Iraqi Prime Minister Haider al-Abadi last month said 2016 will be the year of "final victory" on the hard-line group.